The Development and Application of High Performance Water Base Muds for HTHP Wells in Yingqiong Basin

High temperature and high pressure deep wells drilled in Yinggehai penetrated formations with narrow density windows.Conventional polymer sulfonate drilling fluids become highly viscous and difficult to flow in complex geological environment, and false thick mud cakes are generated. These generally result in resistance to drill pipe tripping, pipe sticking and lost circulation. A high performance water base drilling fluid has been formulated in laboratory with new high temperature polymers replacing conventional polymers. Laboratory evaluation shows that the high performance water base drilling fluid with density 2.50 g/cm³ maintained its thermal stability for a long time at 240℃, was resistant to the contamination caused by 50 g/L drilled cuttings, 50 mL/L formation water and 5 g/L CO₂, and performed well in reservoir protection, the return permeability reaches 84.6%. This high performance drilling fluid has been used on a well in Yinggehai with formation pressure coefficient of 2.20~2.40 and formation temperature between 190℃ and 200℃, which conventional polymer sulfonate drilling fluid has failed the drilling operation previously. This proved that the high performance water base drilling fluid had good high temperature stability and superior rheology. The successful application of the high performance drilling fluid has provided an reference for selecting drilling fluids for HTHP complex well drilling.